KR20140028077A - Part having a dlc coating and method for applying the dlc coating - Google Patents

Abstract

The present invention relates to a component having a WC-C composition gradient layer, excluding a metal-containing underlayer, and having a layer other than an ion implantation layer and a DLC surface layer, wherein the component has a cohesive tendency upon scratch inspection. It features.

Description

PART HAVING A DLC COATING AND METHOD FOR APPLYING THE DLC COATING}

The present invention relates to the technical field of diamond-like carbon (DLC) coatings, in particular DLC coatings for frictional parts.

The invention relates to, for example, friction coefficients such as piston rods, camshafts, valve lifters, cylinders, piston rings and the like, and more generally under load friction. Has a particularly useful application in reducing the coefficient of friction in all cases. To reduce this friction, one skilled in the art is fully aware of the possibility of applying a DLC coating to the part in question.

The invention may also have application in cases where a surface provided by the coating is required to have a black color without other attempts to reduce friction.

It is generally known to those skilled in the art that low adhesion of DLC films on components can be a real problem for certain applications. One technical solution for increasing adhesion is to use a metal-containing adhesive layer based on, for example, silicon or chromium. Various technical solutions are presented.

For example, WO2011 / 018252 describes a friction part having a coating consisting of an adhesive layer, a metal-containing DLC coating and a metal free DLC coating. The adhesive layer is preferably a chromium coating with a maximum thickness of 1 μm while the metal-containing DLC coating is preferably made of WCC tungsten carbide. The ratio of the thicknesses of the various layers and coatings is limited to a specific range of values. Outside this range, if the DLC thickness is too thin, the life of the part will be short, and if the DLC thickness is too thick, the part will peel off or peel off too early. There is a risk.

WO0179585 describes a multilayer system having an adhesive layer, a transition layer and a layer of diamond-like carbon. The adhesive layer comprises elements and silicon in the fourth, fifth or sixth subgroup, while the transition layer comprises carbon and at least one element and silicon in the fourth, fifth or sixth subgroup. The upper layer is mainly made of diamondic carbon. The system has a hardness of at least 15 GPa and a bond strength of at least HF3.

In general, it has been found that a DLC film is delaminated from an undercoat associated with internal stresses in the DLC film and the delamination increases the thickness of the film. It is also apparent that the adhesive underlayer film is formed in individual steps, which increases the cost of the method and makes the method more complicated.

The present invention aims to overcome this problem in a simple, reliable, effective and efficient manner.

The problem to be solved by the present invention is to produce a DLC film having improved adhesion without using a metal-containing adhesive underlayer film (eg, silicon or chromium) based on the teachings of the prior art.

In order to solve this problem, metal parts having a WC-C composition gradient layer, no metal-containing underlayer film, characterized by cohesive propensity upon scratch inspection and having a DLC surface layer have been designed and completed.

The invention is explained in more detail with reference to the accompanying drawings in which: FIG.
1 is a diagram showing a fracture profile of a coating using the scratch test method.
FIG. 2 is a cross-sectional view along the line AA in FIG. 1 in the case of adhesive flaking.
3 is a cross-sectional view along the line AA in FIG. 1 in the case of cohesive flaking.
4 is a cross-sectional view along the line AA in FIG. 1 in the case of cohesive / adhesive flaking.

The problems mentioned are advantageously solved by the following method:

Microwave etching the part;

Having the part have a WC-C composition gradient layer;

Using a microwave plasma to apply a DLC coating to the WC-C layer;

Microwave etching makes it possible to obtain more effective etching (regardless of the geometry of the part being processed) using diode etching, which regulates the flow of ions. It is also possible to etch parts at low tempering temperatures without degrading the quality of the parts. It has also been observed that microwave DLC coatings can reduce the process time of application by up to about 50% compared to conventional DLC coatings.

Preferably, an argon plasma is made for etching in the pressure range of 0.05 to 0.5 Pa.

In another embodiment, a magnetron PVD technique is used to create a gradient layer of the WC-C composition. Start with a pure WC layer and produce a ramp of hydrocarbon gas, such as C ₂ H _2, and finally produce a WC-C layer. The thickness of the WC-C composition gradient layer is from 0.3 to 10 μm, preferably 0.8 μm for most applications, except that a larger thickness, such as a piston ring, is required.

According to another embodiment, the DLC coating has a thickness of 1 to 20 μm.

The invention also relates to a friction portion having a DLC coating applied to a WC-C composition gradient layer possessed by a microwave-etched portion.

As indicated above, the prior art is obtained in all cases for the purpose of assuring the adhesion of a deposited DLC in which a tungsten-doped DLC layer is subsequently doped with metal, for example, followed by an adhesive underlayer film made of pure Cr. A DLC coating is described that includes a tungsten carbide-based layer that gradually increases in carbon content until loss.

In connection with the present invention, experiments were conducted to compare the results obtained by producing DLC coatings with one or more adhesive underlayers and DLC coatings without the use of adhesive layers in accordance with aspects of the present invention.

Materials were deposited on a pre-ion etched metal-containing substrate to remove any surface oxides to improve the adhesion of the coating. Various ion etching techniques, mainly diode etching, triode plasma etching and ECR microwave etching, are well known to those skilled in the art.

Diode etching involves applying a negative voltage of several hundred volts (<-500 V) to the substrate under an argon atmosphere at a pressure of 1 to 10 Pa. Under these conditions, there is a luminous discharge around the part and argon cations in the plasma bombard the surface of the substrate to achieve surface sputtering and removal of oxides.

Using triode plasma technology, dense argon plasma at low pressure (0.1 to 1 Pa) is generated by a plasma amplifier. Argon cations accelerate by negatively biasing the substrate and they etch the surface. For this type of method, the negative voltage should be a value between -250 V and -500 V to achieve maximum etching efficiency.

ECR microwave etching enables argon plasma generation in the pressure range of 0.05 to 0.5 Pa. The part is deflected from -50 V to -250 V for optimum negative voltage.

Each of these etching techniques was used in this experiment. After etching, a pure chromium adhesive underlayer was produced on a portion of the test pieces by magnetron cathode sputtering to obtain a chromium thickness of approximately 0.1 to 0.2 μm. Tungsten carbide was then deposited on all specimens by magnetron cathodic sputtering, which gradually increased the hydrocarbon flow rate to enrich the deposited carbon to an atomic concentration of over 50% to enable adhesion of the final DLC coating. With the exception of Examples 9 and 10 where the thickness of the tungsten-containing layer increased to 1.5 μm, the tungsten-containing layer had a thickness of approximately 0.5 μm and the DLC had a thickness of approximately 2 μm.

The experimental conditions are summarized in the table below.

Etching technology Presence of Cr Adhesive Layer diode Yes diode no Triode Yes Triode no ECR Yes ECR no

All coatings were specified in terms of adhesion. The scratch test method was used. It will be appreciated that this method involves scratching the material surface deposited with diamond as used for HRC indentation experiments. Gradually increasing loads are applied while the specimen is translated and moved at a constant speed under the diamond. This makes it possible to obtain increasing-load scratches (FIG. 1) and to determine the peeling force (critical load) as well as the peeling scheme on the basis. The peeling mode indicates the breaking point of the coating. There are two main types of peelings:

Adhesive peeling (FIG. 2)

Cohesive peeling (FIG. 3)

There is a mixing method that combines cohesive failure and adhesive failure, referred to as cohesion / adhesion (FIG. 4).

Adhesive peeling coincides with the propagation of cracks along one interface, so that it is parallel to the surface of the part while cohesive peeling propagates through the coating at an oblique angle to the interface. Adhesive peeling is characterized by a lack of adhesion of the coating. Cohesive peeling occurs when the stress exceeds the rupture limit (mechanical strength) of the materials that make up the coating.

In the case of the adhesive side, the critical load imparts the properties of the adhesion.

In the case of cohesive failure, it is not its adhesion but the breaking strength of the characterized coating. Critical loads are not only characteristic of the deposited material, but also the thickness and hardness of the substrate.

The second method was used to assess adhesion. The method involves indenting the deposited material using Vickers diamond under a load of 2 kg.

The table below is obtained on a substrate made of tool steel (hardness 64 HRC) with a total deposition thickness of 2.5 μm without chromium underlayer and 2.7 μm with chromium underlayer and a total thickness of 3.5 μm for Examples 9 and 10 Summarize a series of experiments that include scratch test results. Examples 11 and 12 have thick stacks that can demonstrate the robustness of the present invention. Example 11 includes a 4 μm thick tungsten-based layer deposited over a deposited 8 μm thick DLC. For Example 12, the thickness of the tungsten layer increased to 9.7 μm and the thickness of the DLC surface layer increased to 19.2 μm.

Example Etching technology Presence of Cr adhesive layer Etching pressure
(Pa) Critical load (N) Facies 2 kg (20 N)
Vickers Indent One. diode Yes 2 32 C NTR 2. diode no 2 6 A NTR 3. Triode Yes 0.6 33 C NTR 4. Triode no 0.6 8 A NTR 5. Triode no 0.4 18 CA NTR 6. ECR Yes 0.5 32 C NTR 7. ECR no 0.5 18 CA NTR 8. ECR no 0.3 31 C NTR 9. ECR no 0.3 36 C NTR 10. ECR no 0.3 35 C NTR 11. ECR no 0.3 44 C NTR 12. ECR no 0.3 55 C NTR

C = Cohesive

A = Adhesive

CA = Cohesive / adhesive

NTR = No detachment of deposited material

The above table shows that when the etching of the diode and the prior art instructions, the chromium underlayer film can obtain a strong adhesion at the interface between the WC and the steel (Example 1), in the absence thereof, a strong adhesion can not be obtained (Example 2) Indicates.

The use of triode etching techniques results in a change in the action of the deposited material when scratched without the chromium underlayer (Examples 4 and 5). Critical loads increased compared to diode etching (Example 2) and delamination type changed (Examples 4 and 5).

The flakes observed represent an intermediate peeling mode.

The use of the ECR microwave etching technique, according to the present invention, demonstrates that a mechanical action can be obtained which is quite similar to the prior art without chromium underlayer (Example 8). As with the triode etching technique, it can be seen that reducing the pressure results in improved scratch inspection performance (Examples 7 and 8).

Examples 9 and 10 show that the resistance to cohesive peeling increases by the thickness of the tungsten-containing underlayer film, as evidenced by the critical load values. In both embodiments, the tungsten carbide and gradient layers are 1.5 μm thick. In particular, in Example 9, the tungsten-carbide thickness increased to 1 μm and the thickness consistent with the carbon concentration gradient was 0.5 μm. In Example 10, the tungsten-carbide thickness is 0.2 μm while the carbon concentration gradient layer is increased to 1.3 μm.

Examples 11 and 12 show the firmness of the solution. It is known that increasing the thickness of the thin cured layer deposited in vacuum increases the internal compressive stress. Nevertheless, the action during the scratch test remains coherent and the increase in critical load is the result of an increase in the thickness of the tungsten-based layer.

In addition to the etching technique, when the etching pressure is reduced, the result tends to improve the adhesion of the layer produced without the chromium underlayer. The decrease in pressure during etching depends on the actual technology itself. Diode technology generally does not produce plasma pressures as low as 0.5 Pa.

Thus, the use of a suitable etching technique, according to the present invention, is to reduce the argon pressure and produce an adhering stack of the DLC type without a chromium underlayer—a widely accepted one of ordinary skill in the art and prior technical solution. Enable achievements against

The method according to the invention has many advantages:

It also simplifies the required apparatus and reduces its cost, removes one interface besides removing the adhesive underlayer, thus improving the reliability and robustness of the coating.

In addition, as shown in the experiments conducted, chromium underlayers are materials deposited with chromium underlayers, unlike tungsten carbide, which appears to require more effective etching, which masks defects in certain types of etching to perform as well as in terms of adhesion. It is obvious that there is a tendency.

In addition, the use of Vickers identation with a 2 kg load has no difference in the adhesion of various types of deposition materials. Although the applied load was 2 kg (20 N), the deformation caused by Vickers diamonds was insufficient to cause separation of the deposited material even when defects of adhesion were demonstrated by the scratch inspection method as in Example 2.

Claims (9)

A metal part, characterized in that it has a layer having a WC-C composition gradient and a DLC surface layer characterized by agglomeration propensity upon scratch inspection, and lacking a metal-containing underlayer and an ion implantation layer. The component of claim 1, wherein the component is covered with a DLC coating applied to a WC-C composition gradient layer having a microwave etched portion. A method of applying a DLC coating to a metal part, comprising the following steps:
Microwave etching the part,
The part has a WC-C composition gradient layer,
Using microwave plasma to apply a DLC coating to the WC-C layer. 4. The method of claim 3, wherein an argon plasma is produced for etching at a pressure in the range of 0.05 to 0.5 Pa. 4. The method of claim 3, wherein the WC-C composition gradient layer is produced by magnetron PVD. 6. The method of claim 5, starting with a pure WC layer first to produce a hydrocarbon flow ramp, and finally producing a WC-C layer. Method according to claim 5 or 6, characterized in that the thickness of the WC-C composition gradient layer is from 0.3 to 10 μm, preferably 0.8 μm. The method of claim 3, wherein the DLC coating has a thickness of 1 to 20 μm. A component covered with a DLC coating obtained using the method of any one of claims 3 to 8, characterized by having a metal-containing underlayer film, an ion implantation layer and a WC-C composition gradient.

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